The present invention relates generally to a method for analyzing a first signal indicative of a property of an electrical utility power system, and more particularly to a method for determining the cause of a power system event.
Generally, electrical power originates at a generation station and is transmitted to a load by a system of conductors and other equipment that make up an electrical power system. The equipment that makes up an electric power system can include switches, reclosers, insulators, capacitors, and the like. Over time, or as the result of some particular cause such as contact of a conductor by vegetation, apparatus can cease to operate normally or fail. Sometimes a failure of apparatus results in an abnormally high current that can further damage the power system or injure end users or damage end use devices and equipment. Failures also sometimes result in degraded power quality or loss of electric service.
There are known devices within an electric power system that can function to protect the system and end users from high current. For example, a relay or recloser may be configured to operate to interrupt current flow when the amplitude of the current exceeds a minimum threshold for a minimum duration. When a threshold is met, the device operates and power is interrupted. In many cases the device operates to restore power after a predetermined time period has elapsed. If the failure is still present, a threshold may be met and power interrupted again. In this manner several power interruptions can result from the same cause, either in close succession or spread over an indeterminate period of time. In other cases, failure of a particular apparatus is the actual cause of the power outage and the power remains interrupted until a repair or replacement is made. In some other cases, the faulty apparatus may continue to operate in an abnormal fashion without causing any outage but instead may cause disturbances that may affect the normal functioning of other equipment present in the power system.
When an outage occurs, failing or failed apparatus often must be repaired or replaced before normal, reliable service can be restored. Temporary faults may be cleared and electrical power restored by normal operation of a protective device, i.e., a recloser. However, if the underlying failure or condition remains, power may be interrupted again, either immediately or after an indeterminate amount of time. When sustained outages occur, electrical power system operators such as utility companies must make repairs, and these repairs often must be made at times and under conditions that cause additional difficulties and expense in manpower and equipment. Repairs made in this manner are often more troublesome and expensive than if they could have been planned in advance. In addition, if repairs can be made before a power outage occurs, overall service is more reliable and of higher quality, and inconveniences and economic losses to end users may be minimized or avoided. Therefore it is desirable to identify failures, incipient failures, and other improper or suboptimal operation of power system apparatus before these conditions affect power quality or cause momentary interruptions or sustained power outages.
Utilities may utilize conventional methods to reduce the number of power interruptions and outages that occur. Conventional methods include a) physically examining and/or testing individual apparatus periodically in an effort to determine whether they are likely to fail and cause a power outage or power quality problems and b) replacing apparatus according to a predetermined schedule. Problems exist with both of these approaches. One significant problem is that examining, testing, and/or replacing large numbers of individual devices can be time-consuming, expensive, and difficult to schedule without interrupting power to the end users. A problem with the second approach is that, when apparatus are replaced according to a predetermined schedule, they may be replaced when they are functioning normally, well before any failure actually begins. Alternatively, they may not be replaced in time to avoid an outage. Further periodic maintenance or replacements actually can inadvertently introduce problems that did not previously exist. Clearly it would be preferable to know when apparatus are beginning to deteriorate or operate improperly or sub optimally, so that repairs or replacements could be made prior to actual failure.
In an effort to identify failing or failed devices, utilities may monitor the operation of an electrical power system by monitoring one or more signal indicative of properties such as current. However, conventional methods of monitoring properties of a power system are generally unable to determine that devices are failing before a power interruption or outage occurs. One reason is that conventional methods are generally unable to distinguish relatively small changes that failing apparatus may cause from normal deviations of the property. Another problem with conventional monitoring methods is that human experts skilled in the art of using monitored properties to identify failed or failing devices generally must analyze real-time or near real-time data obtained from a power system. These experts may not be available for analysis when needed and analysis can be expensive and error prone. Yet another problem with conventional methods is that much of the data collected may correspond to normal day-to-day operations of the power system, while only a very small fraction of data thus collected will correspond to abnormal operations caused by failing or failed apparatus. It may not be feasible to manually analyze such huge amounts of data in a timely and reliable fashion.